Electrocoating process with terminal showering step



1967 V G. L. BURNSIDE ET AL 3,360,400

ELECTROCOATING PROCESS WITH TERMINAL SHOWERING STEP 2 Sheets-Sheet 1 Filed July 1, 1965 Jan. 24, 1967 G. BURNSIDE ETAL Filed July 1, 1965 2 Sheets-Sheet 2 60/200 6. JT/FOJEE/PG INVENTORJ United States Patent 3,300,400 ELECTROCOATING PROCESS WlTH TERNHNAL SHOWERING STEP Gilbert L. Burnside, Leopold A. Madejczyk, and Gordon G. Strosberg, Oak Park, Mich., assignors to The Ford Motor Company, Dearborn, Mich, a corporation of Delaware Filed July 1, 1963, Ser. No. 291,625 4 Claims. (Cl. 204-181) This invention relates to an improvement in continuous coating processes wherein a conductive substrate is coated with an organic film-forming material by electrically induced deposition from an aqueous bath. In particular, this invention relates to method and means for promoting coating uniformity in a continuous or intermittently continuous electropainting process wherein a substantially water insoluble coating is deposited upon a moving workpiece in contact with an aqueous bath. More particularly, this invention is concerned with surface irregularities in an electrocoat which result from leaving a workpiece temporarily stationary and partially submerged in the coating bath.

Objects to be coated are suspended from and transported by an overhead conveyor which, with suitable connecting devices, is constructed and arranged such that the suspended workpieces successively enter the aqueous bath for coating and are withdrawn for further processing such as baking, sanding, finish coating, etc. While being coated the object or workpiece is positively charged and a direct current flow of electrical energy is provided between the workpiece and a negative and grounded coating tank or other electrode. In normal operation the conveyor line will stop at irregular intervals for various periods of time. Objects entering or leaving the bath will frequently come to rest with a lower portion of the object below the surface of the aqueous bath and an' upper portion exposed to the atmosphere. It has been found that such stoppages leave deleterious water line irregularities in the coating if provision is not made to avoid their formation or to effect their immediate removal or overcoat. Subsequent removal necessitates refinishing.

It now has been discovered that the formation of these water line marks or the effect thereof can be effectively eliminated by subjecting the positively charged object to a coating bath shower while emerging from the bath. It also has been discovered that this method of operation effectively covers pinholes, craters, and other surface irregularities which occasionally exist after the normal period of submerged coating irrespective of stoppage of the production line.

Organic coating materials which may be used in the bath include but not by way of limitation alkyd resins, acrylate resins, phenol-formaldehyde resins and various carboxylic acid resins or mixtures of the foregoing with each other or other film-forming materials including binding agents and extenders conventionally employed with water based paints. Such materials may include or be employed with other organic monomers an-d/ or polymers including but not by way of limitation hydrocarbons and oxygen substituted hydrocarbons such as ethylene glycol, propylene glycol, glycerol, carbitol, methanol and various carboxylic acids, ethers, aldehydes and ketones. The film-forming material may include or be employed with pigments, dyes, drying oils, etc. and may be dispersed as a colloid, emulsion or emulsoid.

The organic coating material is dispersed in the bath with the aid of a conventional dispersing agent. These include water soluble ammonium and basic amine salts, polymeric amines, etc. Such materials are described at length in US. Patent 2,530,366 to A. G. Gray and elsewhere in the literature.

r 3,300,400 Patented Jan. 24, 1967 It is one object of this invention to promote coating uniformity in a continuous or intermittently continuous electrocoating process by showering the freshly coated and positively charged objects emerging from the coating bath with liquid from the coating bath or its equivalent issuing from a negatively charged discharge electrode or shower head.

With the foregoing and other objects in view, as will hereinafter become apparent, this invention comprises the methods, combinations, construction, and arrangement of parts hereinafter set forth, disclosed, claimed and illustrated in the accompanying drawings wherein:

FIGURE 1 is a schematic drawingdepicting one embodiment of electrocoating apparatus suitable for use with the coating methods herein described, and,

FIGURE 2 is a schematic, partial cross-sectional view 7 of the apparatus shown in FIGURE 1 illustrating the shower equipment in operation.

Referring now to FIGURE 1, a chemically resistant tank 11 contains an aqueous coating bath 13 and serves as a negative electrode or cathode in the coating process. Tank 11 is electrically connected to DC. power source 17 via conductor 15. An article towbe coated 19, eg an automobile body, is shown suspended from an endless conveyor 23 by a hanger 21. Conveyor 23 may be of the electrically powered, chain driven variety. Hanger 21 includes insulator 25 which insulates article 19 from the grounded conveyor. Contact plate or brush 27 is attached to and in electrical connection with hanger 21. Article 19 is shown approaching bath 13 and in electrical connection with bus bar 29 which in turn is in electrical connection with DC. power source 17 via conductor 31. Tank 11 is also equipped with recycle shower apparatus one unit of which is here illustrated by pump support 35, pump 37, housing 39, housing support 41, upright conduit 43, lower shower head 47, and upper shower head 51.

Referring now to FIGURE 2 an inlet conduit 33 places pump 37 in fluid communication with the bath in tank 11. Outlet conduits 45 and 49 respectively place shower heads 47 and 51 in fluid communication with conduit 43. A second shower unit comprising inlet conduit 63, pump support 65, pump 67, housing 69, housing support 71, upright conduit 73, outlet conduit 75, lower shower head 77, outlet conduit 79 and upper shower head 81 is shown oppositely positioned from the previously described shower unit and near the end of tank 11 from which the coated objects are withdrawn. Pumps 37 and 67 are conventional constant pressure pumps and are conected to a conventional power source, not shown.

In a preferred embodiment each of the shower heads is in electrical connection withtank 11 and hence forms a portion of the negative electrode system. It will be understood that the shower units here shown may be arranged and multiplied as desired in accordance with the coating process with which the same are employed.

The workpiece 19 is here shown emerging from the bath under a constant shower of bath material drawn from the bath through the aforedescribed shower apparatus.

The positive charge imparted to the workpiece while submerged in the coating bath is maintained while the workpiece passes through the shower which is preferably of small or discrete droplets. It is within the scope of this invention to terminate the shower activity when the conveyor is stopped or, in the alternative, to maintain such activity independent of the movement of the conveyor.

The coating of the submerged object within the bath will ordinarily be carried out at a potential in the range of about 500 to 1000, preferably to 500, volts.

The droplet or particle size and intensity of the shower or spray through which the object emerges will be varied in accordance with the particular system taking into account the individual coating bath, its properties, and its composition. An effective amount of spray can be readily determined in each instance by routine testing and adjustment.

The foregoing detailed description of the embodiment shown in the drawings is submitted solely for purposes of illustration. Those skilled in the art will be aware that numerous modifications can be made in the aforedescri bed system Without departing from the spirit and the scope of the invention as expressed in the claims.

We claim:

1. In a method of coating which comprises transporting an electrically conductive object through an aqueous bath having organic film-forming material dispersed therein and a first charged electrode in contact therewith, imparting an electrical charge to said object so that said object serves while in contact with said bath as a second electrode and is of opposite polarity to said first electrode, and providing a flow of electrical energy between said first electrode and said second electrode and through said bath until a substantially water insoluble coating of said organic material is deposited upon said second electrode, the improvement which comprises showering said second electrode with said aqueous bath material as said second electrode emerges from said bath and maintaining said shower until said second electrode is out of contact with said bath.

2. In a method of coating which comprises transporting an electrically conductive object through an aqueous bath having organic film-forming material intimately dis persed therein and a first and negatively charged electrode in contact therewith, imparting an electrical charge to said object so that said object serves while in contact with said bath as a second electrode and is of opposite polarity to said first electrode, and maintaining a How of electrical energy between said first electrode and said second electrode until 'a'substanti'ally water insoluble coating of said organic material is deposited upon said second electrode, the improvement which comprises maintaining said electrical charge on said second electrode as the same emerges from said coating bath and showering said second electrode with discrete droplets of said aqueous bath issuing from a third electrode of the same polarity as said first electrode until essentially all of said second electrode is out of contact with said bath.

3, In a method of coating which comprises transporting an electrically conductive object through an aqueous bath having organic film-forming material intimately dispersed therein and a charged cathode in contact therewith, imparting an electrical charge to said object so that said object serves as the anode of a coating cell while in contact with said bath, and maintaining a flow of electrical energy between said cathode and said anode until a substantially water insoluble coating material is deposited upon said anode, the improvement which comprises providing above the surface of said bath a spray of said bath material issuing from a third electrode of the same polarity as said cathode and passing the charged anode through said spray as it emerges from said bath material.

4. In a method of coating which comprises transporting an electrically conductive object through an aqueous bath having organic film-forming material dispersed therein and a first charged electrode in contact therewith, imparting an electrical charge to said object so that said object serves while in contact with said bath as a second electrode and is of opposite polarity to said first electrode,

References Cited by the Examiner UNITED STATES PATENTS 1,590,601 6/1926 Taylor 204l8l 1,897,902 2/1933 'Harsanyi 204181 1,911,808 5/1933 Collins 204181 2,753,298 7/1956 Gray 204206 JOHN H. MACK, Primary Examiner.

E, ZAGARELLA, Assistant Examiner. 

1. IN A METHOD OF COATING WHICH COMPRISES TRANSPORTING AN ELECTRICALLY CONDUCTIVE OBJECT THROUGH AN AQUEOUS BATH HAVING ORGANIC FILM-FORMING MATERIAL DISPERSED THEREIN AND A FIRST CHARGED ELECTRODE IN CONTACT THEREWITH, IMPARTING AN ELECTRICAL CHARGE TO SAID OBJECT SO THAT SAID OBJECT SERVES WHILE IN CONTACT WITH SAID BATH AS A SECOND ELECTRODE AND IS OF OPPOSITE POLARITY TO SAID FIRST ELECTRODE, AND PROVIDING A FLOW OF ELECTRICAL ENERGY BETWEEN SAID FIRST ELECTRODE AND SAID SECOND ELECTRODE AND THROUGH SAID BATH UNTIL A SUBSTANTIALLY WATER INSOLUBLE COATING OF SAID ORGANIC MATERIAL IS DEPOSITED UPON SAID SECOND ELECTRODE, THE IMPROVEMENT WHICH COMPRISES SHOWERING SAID SECOND ELECTRODE WITH SAID AQUEOUS BATH MATERIAL AS SAID SECOND ELECTRODE ENERGES FROM SAID BATH AND MAINTAINING SAID SHOWER UNTIL SAID SECOND ELECTRODE IS OUT OF CONTACT WITH SAID BATH. 